Document EP-A-0 770 514 describes an example of such a mobile joint mechanism which can remain unlocked even after the control device has been released when the back of the seat is tipped forward, for example in order to gain access to the back seats of a vehicle if the mechanism concerned has been fitted on the front seats of a two-door vehicle. When the seat back is then raised again the mechanism re-locks itself automatically as soon as the first pin comes opposite the corresponding gap in the circular guide.
The mechanism described in this document is entirely satisfactory, but nevertheless has the disadvantage that it always re-locks the seat back at the same angle when the back is raised after having been tilted forward, regardless of the previous adjustment of the said back.
The user of this seat must therefore readjust the back each time he raises it after having tilted it forward.
Moreover, document EP-A-0 694 434 describes a mobile joint mechanism using toothed locking units which allows the seat back to be tilted forward and then automatically re-locks the back in its previously adjusted position. This mechanism works perfectly, but the mechanism's toothed locking units, which allow adjustment of the back, interlock with a toothed gear that is itself mobile in relation to the second flange and which can be fixed to this second flange via other toothed locking units.
In this case both flanges are thus connected by two levels of toothed locking units, which tends to make the mechanism heavier and more complex.